1. Field of the Invention
This invention relates to the field of current-carrying devices and components. In particular, the invention relates to a current-carrying device including a substrate and a conductive layer.
2. Description of the Related Art
Current-carrying structures are generally fabricated by subjecting a substrate to a series of manufacturing steps. Examples of such current-carrying structures include printed circuit boards, printed wiring boards, backplanes, and other micro-electronic types of circuitry. The substrate is typically a rigid, insulative material such as epoxy-impregnated glass fiber laminate. A conductive material, such as copper, is patterned to define conductors, including ground and power planes.
Some prior art current-carrying devices are manufactured by layering a conductive material over a substrate. A mask layer is deposited on the conductive layer, exposed, and developed. The resulting pattern exposes select regions where conductive material is to be removed from the substrate. The conductive layer is removed from the select regions by etching. The mask layer is subsequently removed, leaving a patterned layer of the conductive material on the surface of the substrate. In other prior art processes, an electroless process is used to deposit conductive lines and pads on a substrate. A plating solution is applied to enable conductive material to adhere to the substrate on selected portions of the substrate to form patterns of conductive lines and pads.
To maximize available circuitry in a limited footprint, substrate devices sometimes employ multiple substrates, or use both surfaces of one substrate to include componentry and circuitry. The result in either case is that multiple substrate surfaces in one device need to be interconnected to establish electrical communication between components on different substrate surfaces. In some devices, sleeves or vias provided with conductive layering extend through the substrate to connect the multiple surfaces. In multi-substrate devices, such vias extend through at least one substrate to interconnect one surface of that substrate to a surface of another substrate. In this way, an electrical link is established between electrical components and circuitry on two surfaces of the same substrate, or on surfaces of different substrates.
In some processes, via surfaces are plated by first depositing a seed layer of a conductive material followed by an electrolytic process. In other processes, adhesives are used to attach conductive material to via surfaces. In these devices, the bond between the vias and conductive material is mechanical in nature.
Certain materials, referred to below as voltage switchable dielectric materials, have been used in prior art devices to provide over-voltage protection. Because of their electrical resistance properties, these materials are used to dissipate voltage surges from, for example, lightning, static discharge, or power surges. Accordingly, voltage switchable dielectric materials are included in some devices, such as printed circuit boards. In these devices, a voltage switchable dielectric material is inserted between conductive elements and the substrate to provide over-voltage protection.